Certain structural plastics, such as high impact polystyrene (HIPS), acrylonitrile/butadiene/styrene (ABS) resins, poly(vinyl chloride) (PVC) resins, and the like, exhibit attractive mechanical properties when extruded, molded, or formed into various articles of manufacture. Such articles include, for example, bathtubs, shower stalls, counters, appliance housings and liners, building materials, doors, windows, siding, decking, railings and shutters, lawn and garden applications, marine applications pool application, and storage facilities. Although these structural plastics are strong, tough and relatively inexpensive, the properties of their exposed surfaces are less than ideal. That is, the surfaces of the structural plastics are degraded by light; they can be easily scratched, and can be eroded by common solvents.
Consequently, it has become a practice in the industry to apply another resinous material over the structural plastic to protect the underlying structural material and provide a surface that can withstand abuse associated with the use environment. Such surfacing materials are called “capstocks”.
The capstock generally is much thinner than the structural plastic, typically being about 5 to about 25% of the total thickness of the composite comprising the capstock and structural plastic plies. For example, the thickness of the capstock can be about 0.1 to about 2.5 mm, whereas the thickness of the structural plastic ply can be about 1.0 to about 10 mm.
As a class, acrylic polymers, known for their excellent optical characteristics, resistance to degradation by sunlight, hardness, inertness to water and common chemicals, durability, and toughness, are capstocks of choice for various structural plastics. Such acrylic capstocks are described in U.S. Pat. No. 6,852,405, incorporated herein by reference. U.S. Pat. No. 5,318,737 describes the use of an impact modified acrylic capstock for use over PVC by coextrusion.
Fluoropolymers are known for excellent durability and weatherability, however they suffer from poor adhesion to most polymeric substrates. To overcome this deficiency, blends of fluoropolymer and acrylic polymers have been used to produce a good combination of adhesion to thermoplastic substrates, impact resistance, and processing properties. Blends having 30 to 80 percent fluoropolymer have been described in U.S. Pat. Nos. 5,322,899 and 6,444,311.
Surprisingly it has now been found that acrylic capstocks containing low levels of fluoropolymer exhibit excellent impact resistance and solvent resistance in a capstock formulation.